Heat seal coating (HSC) has been used in food, pharmaceutical, medical, and industrial packaging applications. Examples of HSC products include waterborne ethylene vinyl acetate (EVA)-resin-based heat seal coatings (i.e. ADCOTE 37 series, available from The Dow Chemical Company).
Waterborne HSC products are typically manufactured by a batch dispersion process, which has relatively high conversion cost due to long cycle time as well as substantial batch to batch variations. Significant waxes as process aids are required in the batch dispersion process in order to help dispersibility, and they do not contribute to the adhesion properties.
Therefore, a lower-cost process for manufacturing waterborne HSC products while still maintaining or improving quality and HSC performance, is desired. Additionally, the EVA resin is likely to be subject to hydrolysis in the batch dispersion process due to longer processing in a strong base environment at high temperature, so a continuous dispersion process with short residence time is highly desired to significantly mitigate EVA hydrolysis.